R and spatial data: introduction 2

1 Mapping SEIFA indices in Melbourne - interactive maps

1.1 Quick maps

1.1.1 Code

tmap_mode("view")

## tmap mode set to interactive viewing

SA2_SEIFA %>% 
  qtm(fill = "IRSAD_d")

SA2_SEIFA %>% 
  qtm(fill = "IRSD_s")

1.1.2 Explanation

1.2 Improving choropleth maps

1.2.1 Code

tm_shape(SA2_SEIFA) +
  tm_polygons(col = "IRSAD_d", 
              n = 10, alpha = 0.7, palette = "RdYlGn", lwd = 0)

1.2.2 Explanation

tmaptools::palette_explorer()

1.3 Faceted maps

1.3.1 Code

tm_shape(SA2_SEIFA) +
  tm_polygons(col = c("IRSAD_d", "IER_d"), 
              n = 10, alpha = 0.7, palette = "RdYlGn", lwd = 0) +
  tm_facets(sync = TRUE, ncol = 2)

1.3.2 Explanation

1.4 Proportional symbol map

1.4.1 Code

tm_shape(SA2_SEIFA) +
  tm_borders() +
  tm_bubbles(col = "IRSAD_d", size = "URP", 
             n = 10, alpha = 0.7, palette = "RdYlGn", border.lwd = 0, scale = 0.5)

## Legend for symbol sizes not available in view mode.

1.4.2 Explanation

This type of map uses size of symbols to represent numeric variable on a map.

2 Mapping SEIFA indices in Melbourne - static maps

Interactive maps are great for exploration. On other occasions ‘static’ map can be a better option, for instance when you want to include it in printed report. We will learn how to create one with slightly more advanced use of tmap library functions.

2.1 Quick map

2.1.1 Code

tmap_mode("plot")

## tmap mode set to plotting

tm_shape(SA2_SEIFA) +
  tm_polygons("IRSAD_d", title = "IRSAD deciles", 
              palette = "RdYlGn", n = 10, lwd = 0) 

2.1.2 Explanation

First we instructed tmap package to change from interactive mode into static mode with tmap_mode() function. Notice that rest of parameters is the same as in interactive mode.

2.2 Improving choropleth maps

2.2.1 Code

tm_shape(SA2_SEIFA) +
  tm_polygons("IRSAD_d", title = "IRSAD deciles", 
              palette = "RdYlGn", n = 10, lwd = 0,
              legend.hist = T) +
  tm_scale_bar(position = c("right", "bottom")) +
  tm_compass(position = c("left", "top"))+
  tm_layout(frame = F, 
            main.title = "IRSAD deciles of SA2 areas in Melbourne",
            main.title.size = 1.25, 
            main.title.position = c("left", "top"),
            legend.hist.size = 0.5, 
            legend.outside = T)

2.2.2 Explanation

We have built a map layer by layer, calling different functions and specifying various arguments. We also improved the cartography by providing legend and a histogram (a graph of distribution of values). We specified our data source in tm_shape() function; many parameters indicating how polygons are displayed are specified in tm_polygons() function; we also added north arrow and scale with functions names appropriately; finally tm_layout helped us to put all small details together as legend and title).

Last but not least we saved our map can be saved as file on the disk. That can be done with a call tmap_save(tmap_last(), "path_to_save/name.png"). Notice that we used function inside a finction there to use last displayed map.

3 Further topics

1. Try mapping indices other than IRSAD.

2. Try creating static map with proportianl symbols.

3. Try creating static maps with facets.

4 Resources